The present invention is directed to a method and apparatus for recovery of refrigerant using paired evaporation/condensation processes and specifically to a method and apparatus in which an essentially closed water loop is used to efficiently transfer heat energy from the evaporation process to the condensation process and which further allows excess heat to be purged from the system by evaporation of water in a forced draft condenser.
Ammonia refrigerant is commonly used on large commercial and industrial refrigeration units. The present invention differs from present practice in the industry in that ammonia refrigerant systems requiring service typically vent ammonia directly to the atmosphere. This procedure is no longer possible due to the increased stringency of environmental and occupational safety regulations which limit the amount of ammonia which may be vented to the atmosphere. For larger systems it is, therefore, necessary to provide some means to recover the ammonia refrigerant that does not require venting of ammonia to the atmosphere.
Recovery of refrigerant without venting to the atmosphere involves the recovery of relatively pure refrigerant from refrigerant contaminated with waste materials such as water and oil. The refrigerant is removed from the refrigeration system and introduced to an evaporator. A compressor induces a reduced pressure on the refrigerant in the evaporator which causes the refrigerant to evaporate and be removed as a gas, while the water and oil and other contaminants remain behind in the evaporator where they can be drained off. The compressor transfers the warm gaseous refrigerant to a condenser where it is condensed at a higher pressure to a liquid. The liquid refrigerant enters a receiver from where it can be pumped to a storage vessel or to a refrigeration system. The evaporation of the refrigerant requires the input of heat. In addition, the condensation of the gaseous refrigerant to a liquid produces heat. Furthermore, the compressor adds additional compression heat to the condensed liquid.
There are various patents, primarily in the drying or distillation arts, that employ various means of heat recovery. This is advantageous whenever there exists both vaporization and condensation processes going on simultaneously.
For example, U.S. Pat. No. 4,753,016 issued to Eicholz on Jun. 28, 1988 discloses a condensation process for water vapor under vacuum which is taken from a drying apparatus. The water vapor is condensed into a liquid and heat is recovered from the condensed water for use in the drying process. Additionally heat is recovered from pumps by placing the pumps in an insulated casing where a heat exchanger is used to add this waste heat to the condensed water. This patent does not involve refrigerant recovery and does not employ a closed circuit water loop between evaporation and condensation processes.
U.S. Pat. No. 4,402,795 issued to Erickson on Sep. 6, 1983 is more nearly similar in principle to the present invention. Erickson discloses a means for reducing the energy consumed by thermal separation processes such as distillation. Part of the heat rejected by the process is recovered by a reverse absorption heat pump, then upgraded and returned to the distillation process. This is a complicated process which is necessary due to the need to upgrade the rejected heat before reuse in the process.
U.S. Pat. No. 4,294,664 issued to Anthony on Oct. 13, 1981 discloses a process that captures latent heat of condensation by condensing a process vapor and returning the captured heat to the remaining process liquid for continued vaporization. Anthony has the specific intention of obtaining ethanol from a boiling mixture of wort and water. The ethanol is condensed to a liquid and the heat of condensation is captured to assist in the boiling of the mixture. Anthony employs two loops. One loop employs a refrigerant gas which is compressed to deliver heat to the boiling process liquid and is cooled by a second loop of water. This apparatus is complex and is not adapted to refrigerant recovery.
The prior art does not suggest the use of the heat recovery principle in the recovery of refrigerant nor the use of a single essentially closed loop of circulating water between the evaporator and condenser. The prior art shows various forms of heat recovery in unrelated fields, but not for the recovery of refrigerant working fluids. Furthermore, none of the prior art references show a water loop mechanism of the present invention.
The problems and limitations of the prior art are overcome by the present invention as summarized below.